One feature of a hand-held printer is the random motion printing as compared to a conventional linear-type printer. Most digital printers operate by moving paper under the printing element. This is true for “page printers” which have an active print zone extending across the full width of the paper and true for “serial printers” that also move the print element across the page width in addition to moving the length of the paper by the printing element. This relative movement of paper and print element is a traditional configuration for digital printers. An alternative approach is to fix the position of the paper while the printer element is moved over the paper during printing. An example of this alternative approach is a flat bed plotter where the movement of the print element is controlled by fixed mechanical references along and outside the paper edges. The printer of the present invention is moved manually over the surface of the paper without mechanical linkage and without mechanical control form a fixed reference point. This category of printers is sometimes called a “hand printer” or “random motion printer.” One advantage of this type of category is printer is the potential for compact size which makes it attractive for mobile printing operations.
Because of the effect on resulting print quality, a significant factor in printer design is the accuracy of positioning the print element relative to the page during the printing process. To increase accuracy, position sensors are often adopted to “close the loop” and confirm location. Such sensors typically detect rotation of paper feed rolls or lateral travel of the carrier for the print element. Without precise sensing, small errors can accumulate until the print quality is degraded to an unacceptable level. As such, for a random motion printer it is desired to have an improved ability to determine the position of the print element relative to the paper. Prior hand-held printers in the art have utilized one or more optical sensors to detect typographic structure on paper similar to an optical mouse pointing device. However, such designs can require expensive optical elements and may not always produce reliable results. As such, there is a need for new methods of determining position of the print element relative to the paper. Accordingly, improved hand-held printing devices, systems and methods for using the same are desired.